EAS Publications Series
Volume 9, 2003Magnetism and Activity of the Sun and Stars
|Page(s)||317 - 317|
|Published online||17 November 2003|
J. Arnaud and N. Meunier (eds)
EAS Publications Series, 9 (2003) 317
New evidence for magnetic dynamo processes in young stars
Service d'Astrophysique, Centre d'Études de Saclay, France and
Department of Astronomy & Astrophysics, Pennsylvania State University, USA
A recent observation of the Orion Nebula Cluster with the Chandra X-ray Observatory detected 1075 sources, providing a uniquely large and well-defined sample to study the dependence of magnetic activity on bulk properties for pre-main sequence (PMS) stars descending the Hayashi tracks. The principal result is that X-ray emission does not show the activity-rotation relation which is the dominant correlate of magnetic activity indicators in main sequence stars. Instead, other effects are seen in PMS stars: X-ray luminosities are correlated with stellar bolometric luminosity, mass and size for M < 2-3 M⊙, but the emission drops precipitously in some or all PMS stars with M > 2-3 M⊙. The absence of an X-ray/rotation correlation in PMS stars, and particularly the high X-ray values seen in some very slowly rotating stars, is a clear indication that the mechanisms of magnetic field generation differ from those operating in main sequence stars. The most promising possibility is a turbulent dynamo distributed throughout the convective zone, but other models such as a "supersaturated" α - Ω dynamo or relic core fields are not immediately excluded. The evidence does not support X-ray production in large-scale star-disk magnetic fields. This work is described in detail by Feigelson et al. (2003).
© EAS, EDP Sciences, 2003
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